Selective sorption process



NOV- 22, 1966 E. E. sENsEl. 3,287,432

SELECTIVE soRPTIoN PRocEss Original Filed April l1, 1957 peren/ageUnited States Patent O 6 Claims. (cl. 26o-676) This application is adivision of my copending patent application Serial No. 652,147 filedApril 11, 1957, now abandoned. v

This invention relates to an improved process for separating straightchain hydrocarbon from non-straight chain hydrocarbon in a mixturethereof, and to a manganese-containing zeolite effective in saidprocess.

By straight chain hydrocarbon is meant any aliphatic or acyclic or openchain hydrocarbon which does not possess side chain branching.Representative straight chain hydrocarbons are lthe normal parans andthe normal olens, mono or polyolefins, or straight chain acetylenichydrocarbons. The non-straight chain hydrocarbons comprise the aromaticand naphenic hydrocarbons as well as the isoparans, isoolenichydrocarbons, and the like. Straight chain hydrocarbon-containingmixtures which are suitably treated in accordance with this inventioninclude mixed butanes, mixtures of normal alkanes and their isomers, andVarious petroleum fractions such as naphtha fraction, a gasolinefraction, a diesel oil fraction, a kerosene fraction, a gas oil fractionand the like. Particularly suitable for treatment in accordance withthis invention are straight chain hydrocarbon-containing fractionshaving a boiling point or a boiling range in the range of 40-550" F. andcontaining a substantial amount of straight chain hydrocarbons, e.g.,2-35% by volume. More particularly, a petroleum fraction suitable foruse in practice of this invention could have an initial boiling point inthe range of 40-300 F. and an end point in the range of 15G-550 F. Apetroleum fraction for use in the practice of this invention mustcontain both straight chain and non-straight chain hydrocarbons asdemonstrated by the following composition:

Hydrocarbon type: Percent by volume Typical refinery stocks or fractionswhich are applicable to the practice of this invention are a wideboiling straight run naphtha, a light straight run naphtha, a heavystraight run naphtha, a catalytically cracked naphtha, a thermallycracked or thermally reformed naphtha, a catalytically reformed naphthaand the like.

Heretofore, a synthetic sodium calcium alumino-silicate, a dehydratedcrystalline zeolite, having a ratio of calcium to sodium (measured as amolecular ratio of calcium oxide to sodium oxide) between about 2:1 andabout 4:1 and designated in the trade as Linde 5A molecular sieve, hasbeen proposed for separating certain straight chain hydrocarbons fromnon-straight chain hydrocarbons in a gasiform mixture thereof. Broadly,the empirical formula for such sodium calcium aluminosilicate, indehydrated state, can be Written (ca, Napomzoszsio,

This sorbent can be made by exchanging calcium for some of the sodium inthe sodium form of the type A Fice zeolite, then removing crystal water.Properties and structure of the type A zeolite are described in thearticles of Breek et al. and Reed et al. which appear on pages 5963-5977of the Journal of the American Chemical Society, No. 23, volume 78. Theformula (less crystal water) represented for the sodium form of the typeA zeolite in the above-mentioned articles is N312 (A102) 12- (SOa) 12which is a multiple of six of the empirical mineralogical oxide formulaNa2O.Al2O3.2SiO2. For purposes of simplicity I prefer to use the oxidesort of formula for describing the type A zeolite structure, but it willbe understood that both vkinds of formulae are interchangeable forpurposes of reference herein to zeolites of type A structure, and, wherean oxide formula concluding with Al2O3.2SiO2 is used herein, thematerial being referred to is a type A zeolite.

Capacity and selectivity of said 5A molecular sieve for straight chainhydrocarbons are good, c g., approximately 40-45 cc. of normal butaneper gram of this mineral sorbent at temperature of F. and pressure of760 mm. Hg as against approximately l to 3 cc. of isobutane per gram ofthe sorbent under the same conditions. At room temperature andapproximately atmospheric pressure this mineral sorbent becomes, for allpractical purposes, saturated (i.e., it has no more capacity for agaseous normal paraffin such as normal butane or those of highermolecular weight) after a contact time of about l5 minutes with thestraight chain hydrocarbon vapor. Furthermore, it takes almost 5 minutesto reach 90% of saturation of this sorbent with normal butane at roomtemperature and atmospheric pressure.

It has been proposed, for example, to separate normal butane fromisobutane as one typical operation with said 5A molecular sieve, and toseparate higher normal parafiins land olefins from non-straight chainhydrocarbons in other operations by the process which comprisescontacting the mixture of non-straight and straight chain hydrocarbonsin vapor phase with said 5A molecular sieve, thereby selectively sorbingsome of the straight chain hydrocarbon; withdrawing the resultinghydrocarbon mixture depleted of straight chain hydrocarbons; anddesorbing sorbed straight chain hydrocarbon from the laden mineralsorbent to dit it for reuse. Alternating from sorption to desorption andvice-versa can be done very simply and rapidly by an essentiallyisothermal pressure swing technique. This technique is more fullydescribed hereinafter.

Efficiency of a plant for separation of straight from non-straighthydrocarbon using the contacting process outlined above is a function ofthe mineral sorbents selectivity for, and sorbing and desorbing ratesfor the straight chain hydrocarbons in process. This becomesparticularly evident in the instance of a fixed bed contacting plantwherein a substantial shortening of the sorbing phase of the operatingcycle coupled with only a small reduction in capacity of the mineralsorbent for straight chain hydrocarbons will permit a greater number ofoperating cycles a day and, consequently, will increase the productionsignificantly.

I have now found, in a process for separating straight chain fromnon-straight chain hydrocarbons in a mixture thereof, that use of asynthetic crystalline zeolite of type A structure having 0.25 to 0.95 ofits exchangeable cation content as divalent manganese under certaincontrolled operating conditions hereinafter described can shortensignificantly the sorbing time without a proportional sacrifice insorbing capacity or any significant loss in selectivity. Viewed from oneaspect, my invention permits the processing of a larger quantity ofparticular hydrocarbon 3 mixture to desired specifications with a givenWeight of sorbent than has been possible heretofore. Thus, by contactingthe hydrocarbon mixture with the aforementioned manganese-containingtype A zeolite under vapor phase sorbing conditions, I iind that I canobtain 80-95% of saturation capacity of said zeolite for a straightchain hydrocarbon or hydrocarbons present in a very short time,generally in substantially less than 4 minutes, e.g., 1-3 minutes, andusually in a time as short as l-2 minutes, or even less.

As this sorption of the straight chain hydrocarbon is occurring, thereis withdrawn from sorbing contact a hydrocarbon mixture containing areduced amount of straight chain hydrocarbon. When 80-90% saturation ofmy zeolite with sorbed hydrocarbons has been eiected in Vthe aforesaidshort time, the feed mixture of hydrocarbons is shut off, and the ladenzcolite subjected to desorbing conditions whereby previously sorbedstraight chain hydrocarbon is driven off and the zeolite made readilyfor another cycle.

Not only can sorbing be made materially faster using the aboveprocessing technique and said manganese-con taining type A zeolite (ascompared to using the conventional sodium calcium alumino-silicate 5Amolecular sieve), but also desorbing appears to proceed at acorrespondingly faster rate under comparable desorbing conditions. Forgreatest processing throughput with a given amount of mineral sorbent,desorbing is advantageously discontinued when the zeolite containsstraight chain hydrocarbon material from previous sorbing operationsamounting to roughly l-20% of saturation capacity. Thus, in preferredoperation both sorbing and desorbing is only 80-90% complete, but donevery rapidly with short contact time.

While the hydrocarbon contacting operations with my sorbents areconducted preferably as a cyclic process with a fixed bed of sorbentparticles, it is possible also to use moving or uidized bed contact.This is particularly true when the particles of sorbent are stabilizedby methods described in the following U.S. patent applications, all ofwhich are assigned to The Texas Company: Riordan et al., Serial N o.544,244, tiled on November 1, 1955; Hess et al., Serial No. 544,185,tiled on November 1, 1955; and Ray, Serial No. 599,231, filed on July20, 1956, now U.S. Patent No. 2,947,709.

The preferred manganese-containing sorbents of my invention are mostconveniently prepared by exchanging manganese for sodium in the hydratedsodium form of the type A zeolite, Na2O.Al2O3.2SiO2.4.5HZO, for example,by agitating such hydrated parent zeolite for 1/2 to 12 hours in a 0.1to N aqueous manganese salt solution, discarding the salt solution, andrepeating the treatment with fresh solution until the necessaryproportion of the sodium originally present in the structure has beenreplaced by manganese. Operating at room temperature and pressure tivechanges of aqueous 1 N manganese chloride are usually adequate to obtainsufficient manganese substitution for purposes of practicing myinvention. After calcining or otherwise ridding the resultant sorbent ofWater, it is receptive to straight chain hydrocarbons.

Alternatively, a hydrated sodium-calcium form of the type A zeolite,e.g., the Linde 5A molecular sieve, or a hydrated sodium-lithium orhydrated sodium-potassium form of the type A zeolite, can be treatedwith a manganese salt solution in a similar manner to produce asimilarly useful type A zeolite having 0.25-0.95 of its exchangeablecation content of divalent manganese. The fraction of exchangeablecation content referred to herein is computed as the ratio of the numberof equivalents of divalent manganese to the sum of the equivalent of allthe exchangeable metals, eg., Mn++, Na+, Li+, K+, Ca++ etc., in theresulting type A structure.

Among the manganese salts useful in the ion exchanging are manganesenitrate, chloride, bromide, iodide, fluosilicate, formate, and sulfate.The parent sodium form of the type A zeolite can be made by theprocesses shown in the following U.S. patent applications, both of whichare assigned to The Texas Company: Sensel, Serial No. 617,734, now U.S.Patent N o. 2,841,471 and Estes, Serial No. 6l7,735, now U.S. Patent No.2,847,280, both filed on October 23, 1956.

FIGURE 11 of the drawing shows curves plotted from experimental resultsfinding the percentage of saturation (ultimate capacity) obtained withn-butane at room temrperature (75 F.) and atmospheric pressure forvarious contact times lof .the nJbutane with two selective mineralsonbents, one (Ca2, Na)O.Al2O3.2SiO2, i.e., the Linde 5A molecularsieve, wherein the ratio of Ca to Nag Was about 3:1, 'and the other atypical sodium-manganese type A zeolite of this invention wherein 39% ofthe exchangeable cation content in the structure -Was divalentmanganese. Inspection of the ligure shows that the conventional zeoliteattained only about 73% of saturation with the normal hydrocarbon in 2minutes, whereas the manganese-containing zeolite of my inventionattained about 88% |of sa-turation in 2 minutes. Ultimate capacity ofthe two scribe-nts for n-butane under the test conditions Waspractically the same. N-butane siorbing rate characteristics formanganese-containing type A zeolites having lbroadly 0.25 to 0.95 oftheir exchangeable cation content as divalent manganese andcorresponding to the 'above test zeolite are about the same. However,for economy and efficiency of preparation, those having 0.35-07 of theexchangeable cation content as divalent manganese are preferred.

FIGURE 2 shows curves plotted from experimental results finding straightand non-straight chain :hydrocarbon capacity and selectivitycharacteristics at about room temperature (75 F.) and atmosphericpressure for type A zeolites wherein the content of divalent lmanganesein the zeolite was varied over a wide range. As thesemanganesecontainin-g type A zeolites are made most conveniently andpreferably ilzvy exchanging a portion lof Na+ ions for Mn++ ions in thesodium [60mn of the type A zeolite, the test zeoli-tes were made thatway and the x axis indicates the percentage of sodium replaced bymanganese in the type A structure. The capacities of themanganese-containing ty-pe A zeolites for the non-straight chainhydrocarbon, isofbutane, and the straight chain hydrocarbons, normalbutane and ethane, are indicated on the y axis.

While the foregoing experimental work was done mainly wit-h butane andisoibutane, it will be understood that these two hydrocarbons arerepresenta-tive of the two broad classes of hydrocarbons forpurposes ofthis invention, namely straight-chain and non-straight chainhydrocanbons, and that hydrocarbons `of higher molecular weight, e.'g.,up to about 550 F. nunmal boiling point, can fbe treated similarlyexcept with the reservation that temperature and/or pressure conditionsmust tbe such 'that the hydrocarbons are in vapor phase for sonption.

A convenient and rapid 'Way to chan-ge from sor-hing conditions todescribing conditions in the practice of my process is rto operateessentially isothermally at a temperature ffnom about 50 to about `800"F. and to sonb under a pressure of Ito 2000 p.s.i.1g., then to desonb atlower pressure in the range from 0 to 100 p.s.i.|g. or evensubatmospheric pressure. Such operation is described in U.S. Patent No.2,859,256, of Hess et al., also assigned to The Texas Company.

The pnocess vorf -my invention can also be operated wherein temperatureof sorbin-g contact is 'between 50 and 500 F. and is raised fordesorption. Alternatively, desorption can Ibe done at a temperaturesubstantially' above, and at a pressure substantially lbelow fthes'oribing temperature and pressure to drive off soi-bed straight chainhydrocarbons. Describing can be done advantageously by using aswbatmospheric pressure, eig., 10 to 25 inches of Hg absolute, and/ or asweep of low molecular weight gas, eig., hydrogen, nitrogen, isopentane,or methane to help drive oi described straight chain hydrocarbon vaporsfrom the mineral sorbent.

The following examples show how type A zeolites 'having manganese as aportion of Itheir exchangeable cation content have been prepared and howsuch zeolites can 'be used in a renery, but should not ibe construed aslimiting the invention.

A type A zeolite in which 37% of the exchangeable ca-tion content wasmanganese was made as follows: 50 ,grams of pelleted and dehydratedsodium form tof the type A zeolite, marketed as Linde 4A molecularsieve, was allowed to soak tor 38 'hours at 200 F. in 60 cc. of 3 Naqueous MnCl2 solution. The exchanged zeolite was washed with water anddehydrated at about 575 F. for two hours to prepare it for sorption ofstraight chain hydrocarbons.

A manganese-calcium-sodium form of type A zeolite was made as follows:'30 grams of granular dehydrated calcium-sodium form of t-ype A zeolitewas allowed to soak in 72 cc. of 4.5 N aqueous MnCl2 solution at 200 F.for 184 hours. The ygranules were washed thoroughly 'with Wa-ter anddehydrated .to remove zeolitic water. Chemical analysis of the productzeolite indicated a for-.mula (dehydratedv state) as follows: (0.5Mn,0.35Ca, 0.15Na2)O.A12O3.2SiO2. Capacity of the product at 75 F. andatmospheric pressure, found by test, was 45 cc. of ethane per gram, 39cc. of n-butane per gram, and 4 cc. of isobutane per gram.

One-half of the product produced in the immediately previous ionexchanging operation was treated for a second .time with 72 cc. of 4.5 Naqueous `MnClZ solution at 205 F. for 83 hours. The granules were washedthoroughly with water, and dried to remove water. Chemical a-nalysisindicated the following formula (dehydrated state) (0.75Mn, 0.14C-a,0.11Na2)O.A12O3.2SiO2. Capacity of the product at 75 F. temperature andatmospheric pressure, found by test, was 44 cc. of ethane per igram, 41cc. of normalbutane per tgrarn, a-nd 4 cc. of isohutane per gram. Thethree foregoing products were capable of attaining from 80-90%saturation with normal butane at room temperature (75 F.) andatmospheric pressure in `substantially less than 4 minutes.

A typical hydrocarbon separation contemplated with mymanganese-containing formof type A zeolitie is the removal of straightchain hydrocarbons :from stabilized, catalytically reformed motornaphtha, such naphtha having characteristics, for example, of APIgravity, 48.8; refractive index (20 C./4 C.), about 1.444; ASTMdistillation IBP., 126 F. and EP., 377 F.; and ASTM research clearoctane rating, 87.1.

The naph-tha in vapor form is passed through a first lbed of mymanganese-containing type A zeolite in -pelleted form at temperature ofabout 750 F., and under pressure of about 350 p.s..g. for 2 minutes. Thezeolite has 35- 70% of its exchangeable cation content manganese withbalance of sodium. Saturation of the pellets with straight chainhydrocarbon components is .tiren about 85% complete. The unsorbednaphtha vapors emerge from the bed low in the straight chain hydrocarboncontent which detracts from the octane rating of the feed stock. At thispoint the naphtha feed is shunte-d t-o another similar sorbent bed. Astream of recycle hydrogen from catalytic reforming of the feed napfhthais passed through the rst bed, briefly under elevated pressure to purgethe vessel of unsorbed material. Then -the pressure on the tirst lbed isreduced to O p.s.i.|g. and the hydrogen is continued for about 2 minutesto -desorb all but approximately l5-20% of the straight chainhydrocarbons in the laden sorbent pellets. The effluent vapors from thedesorbing operation are used as part of the recycle feed to the naphthareforming process.

I claim:

1. Process for `the separation of a straight chain hydrocarbon from an-on-straight chain Ihydrocarbon in admixture therewith which comprisescontacting said admix- .ture in vapor phase with a dehydratedcrystalline Zeolite of type A structure having 0.25 to 0:95 of itsexchange- `able cation content as divalent manganese to adsonb saidstraight chain hydrocarbon therefrom, discontinuing said contact whenabout Ito albout 95% of the saturation capacity of said crystallinezeolites or said straight chain hydrocanbon is reached, desorbing saidyadsorbed straight chain hydrocarbon, discontinuing `said desonbing whenabout 80-90% of the adsorbed straight chain hydrocarbon has beendescribed and repeating said contacting and desorbing steps.

2. Process as claimed in claim 1 wherein contacting is carried out toadsorib from about 8O to about `90% of the saturation capacity of saidzeolite for said straight chain hydrocarbon.

3. Process as claimed in claim 1 wherein desorbing is carried out todesonb from about 80 Ito about `85% orf the adsorbed straight chainhydrocarbon from said zeolite.

4. Process as claimed in claim 1 wherein the mixture is in contact withthe selective adsorbent for a period not in excess of about 5 minutes.

5. Process as claimed in claim 1 wherein contacting is carried ou-t at atemperature between about 50 and 800 F., and a pressure between about100 and 2000 p.s.i.fg.

6. Process as claimed in claim 5 wherein contacting and desorbing arecarried out under substantially isothermal conditions and the describingpressure is less than the contacting pressure.

References Cited by the Examiner UNITED STATES PATENTS 2,859,256 11/1958Hess et al. 260-676 2,882,243y 4/1959 |Milton 26o-676 2,988,577 6/1961sensel 26o-67s 2,988,502 6/1961 Richards er a1. 26o- 676 ALPHONSO D.SULLIVAN, Primary Examiner.

PAUL M. COUG'HLAN, Examiner. D. S. ABRAMS, Assistant Examiner,

1. PROCESS FOR THE SEPARATION OF A STRAIGHT CHAIN HYDROCARBON FROM ANON-STRAIGHT CHAIN HYDROCARBON IN ADMIXTURE THEREWITH WHICH COMPRISESCONTACTING SAID ADMIXTURE IN VAPOR PHASE WITH A DEHYDRATED CRYSTALLINEZEOLITE OF TYPE A STRUCTURE HAVING 0.25 TO 0.95 OF ITS EXCHANGEABLECATION CONTENT AS DIVALENT MANGANESE TO ABSORB SAID STRAIGHT CHAINHYDROCARBON THEREFROM, DISCONTINUING SAID CONTACT WHEN ABOUT 80 TO ABOUT95% OF THE SATURATION CAPACITY OF SAID CRYSTALLINE ZEOLITES FOR SAIDSTRAIGHT CHAIN HYDROCARBON IS REACHED, DESORBING SAID ABSORBED STRAIGHTCHAIN HYDROCARBON, DISCONTINUING SAID DESORBING WHEN ABOUT 80-90% OF THEADSORBED STRAIGHT CHAIN HYDROCARBON HAS BEEN DESORBED AND REPEATING SAIDCONTACTING AND DESORBING STEPS.